The related applications, identified above, set out fully the background of the invention and prior art of this invention. The following description briefly sets out some of the background and prior art of the invention, set out in said applications;
Ophthalmic lenses serve basically three purposes;
(1) correction of vision defects PA1 (2) protection against mechanical hazards to the eye; and PA1 (3) protection against radiation. PA1 W. h. armistead and S. D. Stookey: "Photochromic Silicate Glasses Sensitized by Silver Halides," SCIENCE, Vol. 144 (1964) pp. 150-154; PA1 G. gliemeroth and K. H. Mader: "Phototropic Glass," Angew. Chem. Internat. Edit., Vol. 9 (1970) pp. 434-445; PA1 A. v. dotsenko et al.: "A Study of the Effect of Copper Ions on the Relaxation Properties of Photochromic Glasses," Sov. J. P. Opt. Technol., Vol. 41 (1974) pp. 395-397; PA1 R. j. araujo: "Photochromic Glasses," Chapter 8 of the book PHOTOCHROMISM edited by G. H. Brown, Willey Interscience, New York (1971) pp. 667-686; PA1 H. bach and G. Gliemeroth: "Phase Separation in Phototropic Silver-Halide-Containing Glasses," J. Amer. Cer. Soc. (1971) pp. 43-44. PA1 1. the ingredients producing the photochromic or phototropic behavior are silver halide particles uniformly dispersed in a glass matrix; and PA1 2. articles made from these glasses must be exposed to a well defined heat treatment to develop photochromic or phototropic behavior. PA1 1. Glasses of the types listed in Table 1 hereafter are melted following procedures known to those skilled in the art of glass making. PA1 2. Lens blanks are made of these glasses by known methods such as pressing or casting. PA1 3. These articles are exposed to a controlled heat treatment to develop silver halide particles of linear dimensions d falling essentially within the range 5&lt;d&lt;50 nm. The lower limit is required to produce photochromic or phototropic behavior, the upper limit to avoid light scattering unacceptable in ophthalmic products. The total concentration of these silver halide particles which are dispersed uniformly throughout the glass article should be at least 0.005 vol. %. PA1 1. A base glass having a composition in essence in the general system Alk. Oxide--Al.sub.2 O.sub.3 --B.sub.2 O.sub.3 --SiO.sub.2, with addition of halides to the batch, is melted under conditions that allow retention of a sufficient quantity of halides. PA1 2. Lens blanks are made from the glasses by known methods such as pressing or casting. PA1 3. Finished lenses are made from the blanks by grinding and polishing. PA1 4. The finished lenses are exposed to a source of silver ions at elevated temperature in such a fashion that in those parts of the lens where a high degree of phototropic or photochromic behavior is desired the silver concentration is higher than in those parts where a low degree of phototropic or photochromic behavior is desired. PA1 5. The thus treated lenses are exposed to a carefully controlled heat treatment to grow silver halide crystals to a size required for photochromic or phototropic behavior, but not exceeding linear dimensions of 50 nm to avoid the light scattering unacceptable in ophthalmic lenses. PA1 K--coefficient of extinction and PA1 Z.sub.o --thickness of the lens at the location of measurement measured parallel to the direction of the incident beam of light. PA1 whereby K.sub.1 (t) reaches a constant value after approximately 1/2 hour depending upon the glass studied and the precision of the measurement. PA1 with K.sub.i (t)=K.sub.1 (t) during exposure to activating radiation, PA1 K.sub.i (t)=K.sub.2 (t) after removing the activating radiation; PA1 Z.sub.o (x, y) is determined by the prescription values required to provide for correction of vision in each individual case.
The first purpose is accomplished with transparent lenses having refractive powers, and the second purpose is accomplished by providing lenses of the required physical strength. The third purpose of protection against radiation such as ultraviolet light, intense visible light or infrared radiation can be achieved by adding color in or on the glass of the lenses or in or on the plastics or polymers of the lenses.
The colored lenses and their preparation are fully described in the above related applications.
Permanently colored or dyed ophthalmic lenses have a disadvantage of retaining low transmission of light in low levels of illumination, that is in a more or less dark environment. In such low light environments as nighttime driving, conventional sunglasses may be hazardous. It has been found that this particular disadvantage may be overcome to a certain extent, by the many varieties of phototropic or photochromic commercially available glass or plastic lenses. U.S. Pat. No. 3,197,396 describes phototropic ophthalmic lenses, containing silver ions, which are transparent to visible radiation but will darken to exposure to actinic radiation to where the transmission will be about 45% of the original transmissivity. Some of the other prior art directed to ophthalmic lenses includes U.S. Pat. Nos. 3,208,860; 3,548,060; 3,594,198; 3,617,316; 3,703,388; 3,765,913; 3,795,523; 3,833,511; 3,834,912; British Pat. No. 1,275,019; German Pat. No. 2,230,506; and German Auslegeschrift No. 2,256,775.
In addition to the above mentioned patents on photochromic glasses, all containing silver halide particles uniformly dispersed throughout the volume of an article, it is known that Chance-Pilkington Optical Glass Company, England, it marketing a phototropic phospho-silicate glass under a trade name "Reactolite."
Other photochromic glasses sensitized by silver halides are described in general in the following articles:
The prior art glasses seem to have in common:
The literature described glasses appear to differ from each other in the compositions of the base glasses which serve as carriers for the phototropic or photochromic centers. U.S. Pat. No. 3,208,860 describes a phototropic article comprising a silicate glass body having in at least a portion thereof microcrystals of at least one silver halide selected from the group consisting of silver chloride, silver bromide, and silver iodide, with the concentration of said crystals in the portion being at least 0.005% by volume.
U.S. Pat. No. 3,419,370 teaches a preparation of photochromic lenses by diffusing silver ions into the surface layer of a base glass and then exposing the articles to a specific heat treatment. Glass or plastic articles have also been prepared as photochromic materials by coating the substrates with a phototropic coating as described in U.S. Pat. No. 3,875,321 and described in The Journal of the American Ceramic Society (1974) pps. 332-335 under the title "Reversible Optical Density Changes in Composite Layers."
The photochromic or phototropic lenses above described have certain advantages over permanently tinted lenses. Thus because of the reversibility of the photochromic effect such lenses assume a low transmissivity if exposed to ultraviolet or blue light but resume high transmissivity in an environment where low illumination levels of activating radiation prevail. Glass lenses do not appear to lose photochromic properties as do plastic phototropic lenses during extended wear causing degradation of active ingredients.
All presently known photochromic or phototropic lenses have the disadvantage that recovery of high transmissivity takes several minutes. This has been noticed with discomfort and dislike by wearers under such conditions as driving an automobile where low levels of illumination exist inside the car and high levels of illumination may exist outside the vehicle. While it is desirable to reduce the light intensity to the driver's eyes while observing road and traffic conditions, the driver must be permitted to clearly view information presented by instruments on the vehicle instrument panel where a low level of illumination normally exists. Indeed, it may be dangerous to prevent this. A similar type of problem may be found in occupations where sudden changes in the level of illumination from bright to dim occur either (1) by rapid changes in the intensity of the light source or (2) by movement of the wearer of the spectacles from high level of intensity to a darker environment.
Some of the disadvantages have been overcome by the use of eyeglasses with a continuous variation of transmissivity from low at the top of the lens to high over the lower portion of the lens. Lenses with such a permanent gradient in degree of color or tint are now available in commerce, and it is believed that such lenses are prepared by differentially dyeing plastic lenses or by applying a graded color coating over glass lenses by vacuum deposition of absorbing materials. With plastic lenses such color gradient may be achieved by concentration of the dye absorbed by the lens by different areas. For example, a high concentration of absorption prevails at the top and a low concentration at the bottom of the lens.
In U.S. Pat. No. 3,419,370 there is found a statement that a gradient in photochromic behavior across a glass body is attainable by varying the time and/or temperature at different portions of the glass body exposed to an ion exchange medium. According to this patent the ion exchange bath contains, in all instances, silver ions (see Table 2 of the patent). The gradient in photochromic properties is achieved by causing or allowing different concentrations of silver ions to diffuse into the glass. The teachings of the patent, in our opinion, is that glass cannot be made photochromic or phototropic without having been exposed to the diffusion process in the silver containing ion exchange bath prior to the heat treatment required to develop phototropic or photochromic behavior. The base composition of the glasses do not contain any silver ions, nor is there a teaching of a photochromic gradient over ophthalmic lenses.
In our opinion, the state of the art of making ophthalmic lenses uniformly phototropic or photochromic throughout their entire volume can be summarized as follows:
In our opinion, the state of the art of making glass articles with a gradient in photochromic or phototropic behavior as deduced from U.S. Pat. No. 3,419,370 can be summarized as follows: